Abstract: :
Purpose: Determination of minimum requirements for useful mobilityand evaluation of learning effects when performing this taskin eccentric vision.Methods: Mobility performance was assessed under conditionssimulating artificial vision. Normal subjects wearing a portableartificial vision simulator were asked to complete an indoorcourse consisting of 6 randomly positioned obstacles. Five degreesof image resolution (17920, 1991, 498, 221, and 124 pixels)and 3 effective viewing angles (16.5°x11.6°, 33°x23.1°,and 66°x46.2°) were projected on a 10°x7° viewingarea, stabilized at a fixed position in the visual field. First,the minimum requirements needed to reach optimal mobility performancewere established using central vision. Then 3 naïve normalvolunteers were trained to perform the same task using a viewingarea stabilized at 15° of eccentricity in the lower visualfield.Results: Using central vision, mobility performance decreasedsignificantly (p<0.05) for image resolutions below 0.1 pixel/deg2.There was no significant difference between the three viewingangles for greater image resolutions. The 33°x23.1°viewing angle tended, however, to be the best and subjects reportedpreferring it to the others. A viewing angle of 33°x23.1°,containing 498 pixels (0.7 pixel/deg2) was chosen for perceptuallearning in eccentric vision. Subjects adapted quite rapidlyto eccentric viewing. Within the first 10 training sessionserror counts asymptoted. The time to accomplish the mobilitytask stabilized after about 40 sessions, reaching the same valuethan that measured using central vision.Conclusion: These data demonstrate that mobility in known environmentsrequires much less image resolution than other tasks, like reading.This result is in agreement with clinical observations: lowvision patients unable to read, can move surprisingly well infamiliar settings. Performance in unknown, dynamic environmentsshould still be investigated to get a more complete pictureof minimum requirements for useful mobility.